[PATCH] Make svnperms.py work on Windows

Hi dev,

I tried to get svnperms.py going on a windows server (<rolls eyes>),
but needed this patch to do so:

http://svn.haxx.se/dev/archive-2009-04/0668.shtml

It seems that no-one has answered Sergey on his patch submission back
in 2009. (According to haxx.se, that thread ends right there.)

The patch removes a try-import-except-import thing and replaces it with
a straightforward 'from subprocess import Popen,PIPE'. AFAICT that works
almost everywhere and is a good change.

So, if there are no vetos, I'll commit this patch.

Thanks,
~Neels